The invention relates generally to osmotic delivery systems for sustained delivery of active agents in fluid environments. More particularly, the invention relates to a flow modulator for delivering an active agent from an osmotic delivery system in a fluid environment.
FIG. 1 illustrates a prior-art osmotic delivery system 40, as described in U.S. Pat. No. 6,524,305 issued to Peterson et al. The osmotic delivery system 40 includes an enclosure 42 containing osmotic agent 47 and active agent 44. A dividing member 46 forms a partition between the osmotic agent 47 and the active agent 44. A semipermeable plug 48 is inserted into a first opening 45 of the enclosure 42. The semipermeable plug 48 selectively permits fluid to enter the interior of the enclosure 42. A flow modulator 20 is inserted into a second opening 39 of the enclosure 42. The flow modulator 20 allows the active agent 44 to exit the interior of the enclosure 42 while controlling back-diffusion of fluids into the interior of the enclosure 42. When the osmotic delivery system 40 is disposed in a fluid environment, fluid from the exterior of the enclosure 42 enters the enclosure 42 through the semipermeable plug 48 and permeates the osmotic agent 47, causing the osmotic agent 47 to swell. The osmotic agent 47 displaces the dividing member 46 as it swells, causing an amount of the active agent 44 to be delivered to the environment of use through the flow modulator 20.
In the prior-art osmotic delivery system 40 shown in FIG. 1, the outer surface of the flow modulator 20 includes a helical delivery path 32 through which the active agent 44 passes from the interior to the exterior of the enclosure 42. The thread 36 which defines the helical delivery path 32 abuts the interior surface 43 of the enclosure 42 so that the active agent 44 comes into contact with the interior surface 43 of the enclosure 42 as it passes through the helical delivery path 32. The pitch, amplitude, cross-sectional area, and shape of the helical delivery path 32 are selected such that back-diffusion into the enclosure 42 from the fluid environment is minimized. Fill hole 22 and vent hole 24 are provided in the flow modulator 20. When assembling the osmotic delivery system 40, the flow modulator 20 is first inserted in the enclosure 42. The active agent 44 is then injected into the enclosure 42 through the fill hole 22, while gases in the enclosure 42 escape through the vent hole 24. Thereafter, caps 26 are inserted in the holes 22, 24 so that delivery of the active agent 44 occurs only through the helical delivery path 32.
From the foregoing, there continues to be a desire to provide additional reliability and flow modulator capabilities in osmotic delivery systems.